Had the same problem with my W115 today. It opened up fine, but wouldn't close.

I had 12.6 volts at the switch, the switched tested fine with a ohm meter. I checked for power the sunroof motor, only getting 7 volts.. hmm. I used a wire brush and cleaned the terminals on the fuse holder and the switch and that solved the problem. I was now getting 12+V to the motor.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg